How to Read the DOT Date Code and Tell How Old Your Tires Really Are

Every tire sold in the United States carries a DOT (Department of Transportation) serial number molded into the sidewall. Hidden inside that string of letters and numbers is a four-digit code that tells you exactly when the tire was manufactured, right down to the week. Most drivers never look at it, but tire age is one of the leading causes of blowouts and tread separations, even on tires that still appear to have plenty of tread depth remaining.

This guide explains where to find the DOT date code, how to decode it in seconds, what the numbers mean for safety, and when tire age alone should prompt a replacement, regardless of how the rubber looks on the surface.

What the DOT Number Is and Why It Exists

The DOT number is a compliance mark required by the National Highway Traffic Safety Administration (NHTSA) under Federal Motor Vehicle Safety Standard (FMVSS) No. 139. It certifies that the tire meets federal safety standards and provides a traceable manufacturing record that allows NHTSA to issue targeted recalls if a defect is identified in a specific production run.

The full DOT serial number can be anywhere from 8 to 13 characters long. It encodes the plant where the tire was made, an optional tire size code, optional manufacturer-specific information, and the week and year of manufacture. The last four digits are the ones that matter for age purposes.

One important note: the complete DOT number, including the date code, is often molded on only one sidewall of the tire, the inboard (inner) side that faces the vehicle. The outboard sidewall may show only the letters DOT followed by a partial string. If you cannot see four digits at the end of the DOT string on the visible sidewall, you will need to look at the other side of the tire.

How to Find the DOT Date Code on the Sidewall

Follow these steps to locate the date code on any tire:

• Look at the sidewall of the tire for the letters DOT followed by a string of characters. The entire sequence is typically on one continuous line or split across two lines depending on the mold.
• Count from the letters DOT to the right. The full serial ends with four digits. Those four digits are the date code.
• If the outer sidewall shows only DOT followed by two letters and then blank space or a partial string, the complete number is on the inner sidewall. Use a flashlight or phone camera to read it.
• On tires made before the year 2000, the date code was only three digits (week + single digit year). Any three-digit suffix means the tire is at least 25 years old and must be replaced immediately.

Example of a full DOT string: DOT U2LL LMLR 3119. The last four digits are 3119, which decodes to the 31st week of 2019.

How to Decode the Four-Digit Date Code

The four-digit date code follows a simple format: the first two digits are the week of manufacture (01 through 52), and the last two digits are the year.

• 3119 means week 31 of 2019. Week 31 runs from roughly late July to early August.
• 0422 means week 4 of 2022, which falls in late January.
• 5223 means week 52 of 2023, the last week of December.
• 0124 means week 1 of 2024, the very first week of January.

To estimate the calendar month, divide the week number by 4.3 (since there are approximately 4.3 weeks per month). Week 31 divided by 4.3 gives roughly month 7.2, or July. This is close enough for practical purposes.

The week-and-year format was standardized for post-2000 tires by NHTSA as part of the broader FMVSS 139 update. Before 2000, a three-digit code was used: the first two digits were still the week, but the third digit was the last digit of the year, making it impossible to tell a 1989 tire from a 1999 tire without additional context. Any tire with a three-digit DOT suffix is dangerously old and should never remain in service.

How Old Is Too Old: What the Safety Authorities Say

Tire rubber degrades over time through a process called oxidation. Oxygen, ozone, UV light, heat, and the flexing of the tire during use all break down the polymer chains in the rubber compound. This degradation happens even when a tire is sitting in storage and not being used, and it accelerates in hot climates and when tires are parked in direct sunlight.

The degradation is invisible in its early stages. A tire can appear structurally sound and have 8/32 of tread remaining, yet be on the verge of a catastrophic separation because the rubber compounds have hardened and the steel belt adhesion has weakened.

Here is what the main authorities say about maximum tire age:

• NHTSA does not mandate a single federal replacement age, but it acknowledges that many automakers and tire manufacturers recommend replacement at or before 10 years from the date of manufacture, regardless of appearance or remaining tread.
• Ford, General Motors, Chrysler (Stellantis), Toyota, and Nissan all specify in their owner manuals that tires should be replaced after 6 years, with 10 years as the absolute maximum, even if the tire looks fine.
• The British Tyre Manufacturers Association, which many US safety researchers reference, states that tires over 5 years old should be inspected annually by a professional, and tires over 10 years should be replaced unconditionally.
• Michelin and Continental, two of the largest tire manufacturers in the world, recommend replacing tires that are 10 years old from the manufacturing date, and they note that tires should be inspected regularly after the 5-year mark.

The practical rule used by most tire safety professionals in the US: plan for replacement at 6 years, and treat 10 years as an absolute hard limit. In hot states like Arizona, Florida, and Texas, the 6-year threshold is especially important because heat dramatically accelerates rubber oxidation.

Checking the Age of a Spare Tire

Full-size spare tires and compact temporary spares (commonly called donut spares) are often overlooked during routine tire inspections. They sit under the vehicle or in the trunk for years without ever being rotated into service. By the time a driver actually needs the spare, it may be dangerously old.

The same DOT date code decoding method applies to spare tires. Pull up the spare, find the DOT string on the sidewall, read the last four digits, and calculate the age. Many vehicles with original spares from the factory are driving around today with spares that are 8 to 12 years old. If your spare is more than 6 years old, it should be replaced even if it has never been used and still holds air perfectly.

NHTSA has investigated several accidents involving spare tire failures linked to age-related degradation, including cases where a spare blew out shortly after being put into service following a roadside tire change. The spare appeared normal but had been mounted unused under the vehicle for over a decade.

How to Check Tire Age When Buying Used or New Tires

Tire age matters not only on tires already on your car but also when purchasing replacement tires. Both used and new tires can be older than they appear.

When buying new tires from a dealer or online retailer, read the DOT date code on the actual tire before accepting it. Tires can sit in a warehouse or on a shop shelf for one to three years after manufacture before being sold. A tire sold as new in 2026 could have been made in 2023, which still gives you a reasonable service window, but a new tire from 2020 leaves very little time before the 6-year inspection threshold.

• Ask the seller for the DOT date code before purchase, or inspect the tires in person.
• Avoid buying tires that are already 3 or more years old at the time of purchase, since you are starting your ownership with a reduced service window.
• Never buy used tires without first decoding the DOT date code. A used tire with plenty of tread but a manufacturing date of 2015 or earlier is not a bargain. It is a liability.
• Online tire marketplaces sometimes list new old-stock tires at steep discounts. Check the date code on the product page image if it is visible, or ask the seller directly before ordering.

Visual Signs of Age-Related Tire Degradation

While the DOT date code is the only reliable way to know a tire’s age, there are visible signs that an aging tire may be compromised. These signs can appear before or after the 6 to 10 year threshold, depending on storage conditions and use.

• Sidewall cracking: Fine cracks in the sidewall rubber, sometimes called crazing or weather checking, are a direct sign of oxidation. Even shallow cracks indicate that the rubber compound has begun to break down.
• Tread cracking: Cracks appearing in the grooves between tread blocks, not just on the sidewall, suggest advanced degradation.
• Brittleness: If you press on the sidewall and the rubber feels stiff or does not flex naturally, the rubber has hardened due to age.
• Discoloration: A grayish or faded appearance on the sidewall instead of deep black can indicate UV and ozone damage.
• Bulges or blisters: These indicate internal structural failure and are dangerous regardless of tire age.

Any of these signs warrant immediate inspection by a tire professional and likely replacement. However, absence of these signs does not mean the tire is safe if it is more than 6 to 10 years old. The internal degradation that causes belt separation and blowouts is not always visible from the outside.

Frequently Asked Questions

Where exactly is the DOT date code on a tire?

The DOT date code is the last four digits of the full DOT serial number, which is molded into the tire sidewall. The complete serial number, including the date code, is often on the inner sidewall (the side facing the vehicle), not the outer sidewall that is visible when the tire is mounted. If you only see a partial DOT string on the outside, check the inner sidewall with a flashlight. The four-digit date code will be at the very end of the string, after any other characters.

How old is too old for tires?

Most major automakers (Ford, GM, Toyota, Nissan, and others) recommend replacing tires after 6 years from the manufacturing date, regardless of tread depth or appearance. Ten years is the absolute maximum age stated by several tire manufacturers including Michelin and Continental, and NHTSA acknowledges this 10-year outer limit. In hot climates, the 6-year guideline is especially important because heat accelerates rubber oxidation. Always check the DOT date code and replace tires that have reached these thresholds, even if the tread looks fine.

Can a tire look fine but still be unsafe due to age?

Yes. This is one of the most dangerous misconceptions about tires. A tire can have 7/32 of tread remaining and show no visible cracks, yet the internal rubber compounds and belt adhesion may have degraded significantly due to oxidation. The rubber hardens, becomes brittle, and the bond between steel belts and rubber weakens over time. This internal degradation is not detectable by visual inspection from the outside. Tread depth gauges and visual checks do not account for age-related structural failure, which is why NHTSA and tire manufacturers emphasize the manufacturing date, not just tread depth.

Do tires age faster in storage than in use?

Not necessarily faster, but tires in storage still age due to oxygen and ozone exposure, and improper storage conditions can accelerate the process. Tires stored near electric motors, compressors, or in areas with high ozone concentration degrade faster. UV exposure from sunlight is also damaging. Tire manufacturers generally recommend storing tires in a cool, dry, dark location away from ozone sources, in airtight bags if possible, to slow oxidation. Even with ideal storage, the same 6 to 10 year maximum applies. A tire stored in perfect conditions for 10 years is still a 10-year-old tire.

Does NHTSA require tires to be replaced after a certain number of years?

No. NHTSA does not currently have a federal regulation that mandates a specific tire replacement age. However, NHTSA has investigated numerous accidents tied to age-related tire failures and has acknowledged that automaker and tire manufacturer recommendations of 6 to 10 years are reasonable safety guidelines. Several NHTSA safety advisories point consumers to the DOT date code as the primary tool for evaluating tire age. The lack of a federal mandate makes it even more important for individual drivers to know how to read the DOT date code themselves and follow the guidance from the vehicle manufacturer and tire maker.

The Bottom Line

Reading the DOT date code takes about 30 seconds per tire, and the information it gives you is something no tread depth gauge can provide. Find the last four digits on the inner sidewall, decode the week and year, and compare that date against the 6-year inspection threshold and the 10-year absolute limit. Do the same for your spare. If any tire exceeds those limits, replace it regardless of how it looks, because the degradation that causes blowouts and belt separations happens inside the tire, out of sight, long before the rubber shows obvious cracks on the surface.